videotex
The data service Bildschirmtext (Btx) was renamed Datex-J at the beginning of the 1990s following the expansion of its features, and T-Online (Telekom) in 1995 with the opening up to the Internet.
The tasks of the classic screen text are defined in a state treaty. This stipulates that in Btx everyone is entitled to use the content of the information and communications system as a subscriber and as a provider. The prerequisite is that the information and other services for all subscribers or subscriber groups as well as individual messages are stored electronically for retrieval and are retrieved individually using the public telecommunications network and screen text exchanges or comparable technical switching equipment and typically made visible on the screen. This does not include moving image transmission (Art.1 Btx-StV).
Bildschirmtext is an information system of Deutsche Telekom, which offers various possibilities of use. The telephone network and the Datex-P network are used to transmit information. The International Standards Committee of the International Telecommunication Union( ITU) recommended the generic term videotex at the end of 1978. It is subdivided into screen text from Deutsche Telekom, known as interactive videotex, and videotex from radio and television stations, known as broadcast videotex.
Communication in screen text
Screen text enables dialog with a computer or a Btx center. The subscriber is directly connected to the Btx center via the telephone line and can select screen contents page by page using the input keyboard, supported by a search tree structure or a keyword directory.
The amount of information that can be displayed on a screen consists of 24 lines of 40 characters each or 20 lines of 40 characters each( CEPT standard). The total displayable character set consists of 335 font and special characters, 151 graphic characters and 94 freely definable characters. On the screen 32 colors from a color palette of 4096 shades can be displayed simultaneously.
The services are accessed via modems. The communication of the terminals takes place with the screen text centers. The services range from databasequeries to bank transactions and catalog orders. The Btx network provides for the connection of external computers via the Datex-P network. This also gives the Btx subscriber access to private data processing systems, to other networks that can be used by the public, such as the Internet, and to other online services.
The protocols for the Btx computer network are based on the OSI reference model. Layers 1 to 3 are defined in the ITU recommendation X.25. For the other layers 4 to 7, international agreement has not yet been reached. Therefore, national agreements within the framework of EHKP (uniform higher communication protocols) apply for the time being.
The Btx service was discontinued in 1997.